1. Field of The Invention
This invention relates to an extruding die used for the extrusion of metallic materials.
2. Description of the Prior Art
Heretofore, there has been extruding die which is used for the extrusion of metallic mateials having a structure as shwon in FIGS. 26 to 28 fo example.
A conventional extruding die 51 shown in the figures is a port-hole die classified into hollow dies and, has a male die 52 and a female die 53. The male die 52 is provided with a mandrel 52a at the top portion thereof and the female die 53 is provided with a die 53a in the center portion thereof. And an extruding slit 54 having the shape corresponding to a desired shape of extruded material is formed between said mandrel 52a and said die hole 53a.
A chamber 55 is formed between the male die 52 and the female die 53, and ports 57 in communication with said chamber 55 are formed at four places between four bridges 52b provided to the male die 52 and an outer peripheral portion 52c of the male die 52 connected with the female die 53 at one end face of the outer peripheral portion 52c. And a container 58 connected to another end face of said outer peripheral portion 52c of the male die 52 is so constructed as to charge a billet 59, a billet-receiving face 52d of the male die 52 sited on the side of the billet 59 is constructed from a flat surface.
In performing the extrusion of the billet 59 using the extruding die 51 having a structure of this kind, the billet 59 charged in the container 58 with a dummy block (not shown) placed on the backside of said billet 59 is pressed in the rightward direction in FIG. 27 by stem (not shown). Hereby, the billet 59 is pressed onto the billet-receiving face 52d of the male die 52, and flows in four ports 57 accompanying plastic deformation. Subsequently, the billet 59 is pressed out from the extruding slit 54 after passing through the chamber 55. And hollow extruded material is obtained, which has a desired sectional shape (which is decided against the final shape of the product considering thermal expansion and so on) corresponding to the extruding slit 54 as shown with dotted lines in FIG. 26.
However, in the conventional extruding die 51 as described above, the billet-receiving face 52d receives heavy pressure in the axial direction when the extrusion of the billet 59 is performed because said billet-receiving face 52d of the male die 52 has a flat surface as described above, and tensile stress is applied on four bridges 52b which hold the mandrel 52a of the male die 52 and form ports 57 at four places, on the side of the chamber 55 (parts shown with letters "T" in FIG. 28). Therefore, there is a problem in that a crack in said parts of the bridges 52b on the side of the chamber 55 is apt to develop and sometimes induces breakage of the die.